// courtesy of http://ntt.cc/2008/01/19/base64-encoder-decoder-with-javascript.html


var keyStr = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";

function encode64(input) {
   var output = "";
   var chr1, chr2, chr3 = "";
   var enc1, enc2, enc3, enc4 = "";
   var i = 0;

   do {
      chr1 = input.charCodeAt(i++);
      chr2 = input.charCodeAt(i++);
      chr3 = input.charCodeAt(i++);

      enc1 = chr1 >> 2;
      enc2 = ((chr1 & 3) << 4) | (chr2 >> 4);
      enc3 = ((chr2 & 15) << 2) | (chr3 >> 6);
      enc4 = chr3 & 63;

      if (isNaN(chr2)) {
         enc3 = enc4 = 64;
      } else if (isNaN(chr3)) {
         enc4 = 64;
      }

      output = output +
         keyStr.charAt(enc1) +
         keyStr.charAt(enc2) +
         keyStr.charAt(enc3) +
         keyStr.charAt(enc4);
      chr1 = chr2 = chr3 = "";
      enc1 = enc2 = enc3 = enc4 = "";
   } while (i < input.length);

   return output;
}

function decode64(input) {
   var output = "";
   var chr1, chr2, chr3 = "";
   var enc1, enc2, enc3, enc4 = "";
   var i = 0;

   // remove all characters that are not A-Z, a-z, 0-9, +, /, or =
   var base64test = /[^A-Za-z0-9\+\/\=]/g;
   if (base64test.exec(input)) {
      alert("There were invalid base64 characters in the input text.\n" +
            "Valid base64 characters are A-Z, a-z, 0-9, '+', '/',and '='\n" +
            "Expect errors in decoding.");
   }
   input = input.replace(/[^A-Za-z0-9\+\/\=]/g, "");

   do {
      enc1 = keyStr.indexOf(input.charAt(i++));
      enc2 = keyStr.indexOf(input.charAt(i++));
      enc3 = keyStr.indexOf(input.charAt(i++));
      enc4 = keyStr.indexOf(input.charAt(i++));

      chr1 = (enc1 << 2) | (enc2 >> 4);
      chr2 = ((enc2 & 15) << 4) | (enc3 >> 2);
      chr3 = ((enc3 & 3) << 6) | enc4;

      output = output + String.fromCharCode(chr1);

      if (enc3 != 64) {
         output = output + String.fromCharCode(chr2);
      }
      if (enc4 != 64) {
         output = output + String.fromCharCode(chr3);
      }

      chr1 = chr2 = chr3 = "";
      enc1 = enc2 = enc3 = enc4 = "";

   } while (i < input.length);

   return(output);
}